RA is the most common chronic inflammatory rheumatic disease. It affects approximately 2% of the population of developed countries.
RA is progressive and incapacitating, and creates difficult diagnostic problems in its early forms while at the same time calling for specific treatment. Apart from clinical and radiological signs, the rheumatologist currently has at his disposal only rather non-specific biological tests for his diagnosis. The most widely used of these are the Rose-Waaler test and the latex test, which detect rheumatoid factor in 7 cases of RA out of 10. However, the specificity of these tests is very poor, since these factors are detected in most other autoimmune pathologies and even in some healthy individuals.
The presence of autoantibodies directed towards cellular components is the general feature of autoimmune diseases such as RA, systemic lupus erythematosus, scleroderma or polymyositis. Among the many types of autoantibodies identified in these diseases, those specifically present in patients suffering from RA and reacting with an esophageal epithelial antigen were described for the first time by B. J. J. Young et al. in Br. Med. J. 2:97-99, (1979). These autoantibodies were named at the time "antikeratin antibodies". Hitherto, it was commonly accepted that they were directed towards cytokeratins.
These autoantibodies specific to RA are at the present time detected and titrated by indirect immuno-fluorescence (IIF) on transverse cryosections of rat esophagus.
IIF techniques possess, however, drawbacks which limit their use for the routine diagnosis of RA. In particular, they necessitate the use of tissue cryosections, which involves a loss of time and the participation of specialized personnel; in particular, analysis and reliable interpretation of the results can be carried out only by individuals familiar with histology.
It is hence especially desirable to have available purified preparations of the antigens recognized by the autoantibodies specific to RA, and which may be used in standard techniques of immunochemical diagnosis.
G. Serre et al. in Rev. Rhum. 53(11):607-614 (1986) have shown that an antigen defined by these autoantibodies is characteristic of certain cornified malpighian epithelia of mammals. Present chiefly in the stratum corneum of these epithelia, it is expressed, for example, in the human epidermis.
However, hitherto, no success was achieved either in identifying such an antigen precisely, or in purifying it.